1. Field
The present disclosure relates generally to light-emitting diode (LED) bulbs, and more specifically to controlling lumen loss over time in a liquid-filled LED bulb.
2. Description of Related Art
Traditionally, lighting has been generated using fluorescent and incandescent light bulbs. While both types of light bulbs have been reliably used, each suffers from certain drawbacks. For instance, incandescent bulbs tend to be inefficient, using only 2-3% of their power to produce light, while the remaining 97-98% of their power is lost as heat. Fluorescent bulbs, while more efficient than incandescent bulbs, do not produce the same warm light as that generated by incandescent bulbs. Additionally, there are health and environmental concerns regarding the mercury contained in fluorescent bulbs.
Thus, an alternative light source is desired. One such alternative is a bulb utilizing an LED. An LED comprises a semiconductor junction that emits light due to an electrical current flowing through the junction. Compared to a traditional incandescent bulb, an LED bulb is capable of producing more light using the same amount of power. Additionally, the operational life of an LED bulb is orders of magnitude longer than that of an incandescent bulb, for example, 10,000-100,000 hours as opposed to 1,000-2,000 hours.
While there are many advantages to using an LED bulb rather than an incandescent or fluorescent bulb, LEDs have a number of drawbacks that have prevented them from being as widely adopted as incandescent and fluorescent replacements. One drawback is that an LED, being a semiconductor, generally cannot be allowed to get hotter than approximately 120° C. As an example, A-type LED bulbs have been limited to very low power (i.e., less than approximately 8 W), producing insufficient illumination for incandescent or fluorescent replacements.
One approach to alleviating the heat problem of LED bulbs is to use a thermally conductive liquid to cool the LEDS. To facilitate thermal dissipation, it may be advantageous to increase the thermal paths from the LED to the environment.
LEDs may also be susceptible to a loss of light output (i.e., lumen loss) over time. That is, the quantity of light generated by the LEDs may decrease with use, as compared to an initial quantity of light generated by the LEDs. One potential source of lumen loss is the deposition or reaction of contaminants on the lens or casing of the LED. The heat generated during use of the LED bulb may further drive the deposition or reaction of contaminants. The deposition or reaction of contaminates on the LED casing may cause undesirable alteration or even blocking of the light emitted by the LEDs in the LED bulb. Potential contamination sources in an LED bulb include organics found in solder flux or on printed circuitry. In LED bulbs employing a conductive liquid for thermal cooling of the LEDs, the lumen loss problem may be exacerbated, as the circulating conductive liquid may expose the lens or covering of the LEDs to contaminates suspended or dissolved in the liquid.